Radar landmass simulator

ABSTRACT

In a radar landmass simulator having one photographic memory for storing elevation information and another photographic memory for storing reflectivity information, surplus reflectivity storage is used to store multiplying factors for expanding the elevation information. The multiplying factors are combined with the elevation information to extend the range of usable elevations. Since a surplus of reflectivity storage is available, the net effect is to increase the available elevation storage by a factor of three or more with no increase in the size of the memories.

United States Patent Wolff 1 Oct. 24, 1972 [$4] RADAR LANDMASS SIMULATOR3,439,105 4/1969 Ebeling et a1. ..35/10 4 X 72 l t HanslLWolfl Orldo,F1. I 1 "Venn or an a Primary Examiner-Malcolm F. Hubler [7 1Asslsnee: The United Slaw of Amer! I! Attorney-Richard s. Sciascia etal.

represented by the Secretary of the [57 ABSTRACT [22] Filed: June 19,71In a radar landmass simulator having one photo- [211 App] 52, 4 graphicmemory for storing elevation information and another photographic memoryfor storing reflectivity information, surplus reflectivity storage isused to [52] US. Cl. SIS/10.4 store multipmng factors for expanding theelevation "i; information. facom are l l 0 sum u the elevation informaton to extend the range of usable elevations. Since a surplus ofreflectivity [56] Rehnm Cited storage is available, the net effect is toincrease the UNITED STATES PATENTS available elevation storage by afactor of three or more with no increase in the size of the memories.3.291.884 12/1966 Gray...........................35/10.4 3,413,40211/1968 Marrero ..35/10.4 4 Claims, 5 Drawing Figures REFLECTIVITYMEMORY ESFT ECTWY EYGSRI LZ'V ELS SIGNALS 102 I08 I ESE/ELK? H6 H5 paoc' e son I55 1 323? Raga DISPLAY ELEVATION SCALE M CONVERTER H9 EIGHTYone FRAME ELEVATION SIGNALS TWENTY SEVEN SIGNAL LEVELS ELEVATlON MEMORYRADAR LANDMASS SIMULATOR BACKGROUND OF THE INVENTION The invention is inthe field of simulation of ground mapping radars for training devicesand the like.

Among the different approaches to the simulation of radar signals therecording of elevation (topographical) and reflectivity (cultural) datahas so far been most successfully undertaken by using photographicplates as information storage devices which are scanned by a flying spotscanner or equivalent. The derived data is processed into elevation andreflectivity signals to drive a radar display.

A system known as the factored transparency system is used quiteextensively. In this system a pair of photographic plates is used, oneof which contains the elevation data, the other one the reflectivitydata. Data is stored by processing the plate to diflerent densities orshades of gray. A photoelectric read-out system develops signals ofintensities proportional to the density of the spot on the plate beingscanned. One of the serious limitations of this system is a limitedresolution of elevation data that can be readily extracted from thephotographic recording. Noise and other limitations lead to about 29distinguishable levels. Land elevations may vary from below sea level toabove 30,000 feet. Therefore in radar trainers elevation informationmust be encoded in increments of several hundred feet. This has impairedthe resolution, realism, and effectiveness, of prior art radar landmasssimulators used for radar training.

Many efforts have been made to extend the scale of elevation infonnationdisplay to obtain better resolution. Among many other expedients,multicolored transparencies have been used to store elevationinformation. For example, US. Pat. No. 3,028,684 to S. M. Khanna et alteaches the use of three different colors of four different intensitiesin a single transparency to obtain sixty-four permutations of elevationinformation. US. Pat. No. 3,294,891 to .l. J. Antul et al teaches theuse of three different colors in a single transparency as well as theuse of two colors and separate read-out circuitry to store and retrieveelevation information in a coarse-fine relationship. Unfortunately, theuse of these and other prior art expedients such as numerical codes,etc., is penalized by a requirement for increased complexity in thepreparation of transparencies and in recording and read-out equipment.Elaborate color filtering, cross talk eliminating, and informationprocessing means, are required.

Unlike Khanna, Antul, and others, applicant overcomes the lack ofresolution in the elevation information display of prior art simulatorsby recognizing the existence of and utilizing superfluous storagecapacity in the reflectivity information storage device which isavailable in existing simulators. Seven or eight distinguishable degreesof radar reflectivity are adequate to identify the differentreflectivities required in a radar trainer. Therefore, a photographicmemory used for storing reflectivity information only has a surplus ofstorage capability.

Applicant solves the problem of inadequate elevation information storageavailable by providing novel circuitry for utilizing some of thesuperfluous reflectivity information storage available for additionalelevation storage capacity.

SUMMARY OF THE INVENTION To increase the number of distinguishableelevation levels in a radar trainer, the full range of elevations isdivided into several groups. Each of the groups uses the full range oralmost the full range of density levels, for example, range one coversfrom 0 to 2,000 feet; range two covers from 2,000 to 6,000 feet; andrange three covers from 6,000 to 12,000 feet. If the darkest density inthe elevation data plate is used for the lowest elevation the same levelon the elevation data plate could represent 0 feet elevation, 2,000 feetelevation, and 6,000 feet elevation. To distinguish between thedifferent groups (in this case three groups) of elevation, the secondplate which has to carry the reflectivity data is used. The reflectivityinformation can be much coarser than the elevation information, in facteight distinguishable levels of reflectivity information are completelysatisfactory. The reflectivity plate supplies not only the reflectionbut also the group information needed to distinguish between thedifferent groups in the elevation plate. That is, the same reflectivityis represented on the reflectivity plate by three different levels ofdensity depending upon to which elevation group it relates.

Assuming for example, that the reflectivity plate carries 27distinguishable levels of gray the levels from one through ninerepresent nine different reflectivity data for the elevation group. Thegray levels ten through eighteen represent the reflectivity data for thesecond elevation group, whereas the reflectivity gray scales from levelsnineteen through 27 represent the reflectivity data for elevation groupthree.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a functional diagram of theinvention;

FIGS. 2-4 show a circuit schematic of the reflectivity scale convertershown in FIG. 1; and

FIG. 5 is a circuit schematic of the elevation scale converter shown inFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. I illustrates theprinciples of the invention. A light source such as a tube provides ascanning beam which is divided and directed by optical elements 102 and104 into two beams which scan a reflectivity memory 107 and an elevationmemory 109. Memories I07 and 109 are photographic transparencies whereindata is recorded as discrete densities or shades of gray fixed in aframe 106 which may be moved in a plane normal to the scanning beams bymeans not shown. Other equivalent scanning techniques may be used.Generally in a radar training device the memories are scanned insynchronism with the simulated flight of an aircraft housing a radardisplay. Light transmitted through (or reflected by) memories 107 and109 strikes two respective photomultipliers 108 and which develop outputsignals in response thereto. Photographic memories 107 and 109 eachhave, for example, up to 27 density levels, therefore the output signalsfrom 108 and 110 will have up to 27 intensity levels. These outputsignals are inputs to a reflectivity scale converter I12 and anelevation scale converter 1 14 respectively. Converter 112 is arrangedto convert 26 input levels into eight output reflectivity signals andinto three group signals. Three group signals are furnished to theelevation scale converter 114 over a line 115 and the eight reflectivitysignals are furnished to a radar display 116 over a line 1 17. Line" 117and other lines shown may comprise a multiple channel cable. The 27elevation scale levels and the three group signals are combined inelevation scale converter 114 to obtain an output signal having 81values which is forwarded to data processor and radar display 116 over aline 1 19.

As shown in FIGS. 2-4, the reflectivity read-out signal fromphotomultiplier 108 (FIG. 1) feeds into a potentiometric system Pl-P26that can be adjusted for 26 different gray levels and a resistor diodesystem D1- D26 which provides signals up to that gray level which isscanned at any one moment. These signals form one input to a series ofappropriately biased AND circuits A1-A25, one assigned to each graylevel, whereas the other AND circuit input comes via a signal inverterll, [2, 13, etc., from the next higher gray level sigtal line. Thus onlythat AND circuit produces a signal which is associated with the graylevel presently scanned. If, for example, the gray level 4 is scannedthe next higher level 5 does not provide a voltage drop on the resistorin line 5 and the inversion of the potential from line 5 in 14 and thesignal from line 4 feed into an AND circuit A4 which is appropriatelybiased (i.e. by a threshold device) to provide the signal 4'. The systemas shown therefore provides one of 24 signals 1' 8', l 17', and 19' 26'.

The inverted signal from line 9 represents group signal I. That is aslong as the gray level does not exceed gray level 8, a signal I isgenerated.

For gray signal levels 10 17 a group signal [I is generated by an ANDcircuit A9 which is fed by the gray level 9 signal and the inversion ofthe gray level 18 signal.

Finally, the gray signal line 18 provides the group signal Ill.

Since the derived reflectance signals 1' 8, 10 17', and 19' 26' providerespective data and only one of the respective AND circuits provides asignal at any one time they can be combined and provide the eightdifferent reflectance signals a, b, c, d, e, f, g, and h which can beprocessed in a digital system or converted into analog signals that canbe processed the same way the conventional radar landmass transparencysystem processes the data from the reflectance read-out channel.

FIG. shows a preferred embodiment which generates 3 times 27, that is 8]elevation levels from the 27 gray levels of the elevation plate andthree group signals derived from the reflectance plate.

The elevation read-out signal from photomultiplier 110 (FIG. 1) feeds,preferably via a cathode follower system, a potentiometric system Pl P27that is adjusted to provide signals up to the gray level which isscanned at any one moment. These gray level signals are indicated in thedrawing as lines 1" to 27". Signals 1" to 26" provide one signal to 26AND circuits Al A26 that are assigned one each to each line. The otherinput to these AND circuits comes from lines 2" to 27" via inverters ll126', that is at any one time only one of the AND circuits provides oneof the signals 1" to 26. The signal 27' is derived directly from channel27".

Each of the signals 1 to 27" provides the inputs to three AND circuitsAl", Al, Al"", etc. The other input of these three AND circuits isprovided by the group signal lines I, II, and Ill from the reflectivityscale converter circuit of FIG. 2. Therefore, only one of the 8l ANDcircuits associated with the group signals I. ll, and III is providing asignal at any one time and thereby defines definitely one of 81different elevation levels.

All signals thereby derived can be processed through a computer or afierconversion into analog signals in the same fashion in which theprocessing has been done in the previously mentioned system.

Since the signals provided from the read-out to the potentiometricsystems both in the reflectance and in the elevation channels may draw awide range of currents, a cathode follower system may be desirable asthe input system.

Furthermore, since the logic circuitry used in the two scanning systemsdemands identical base levels a signal converter system may be desirableto adjust the signal base and the signal levels of the I, ll, lIIsignals to be compatible with the l to 27" signals.

The 81 levels of elevation do not have to represent equal intervals. Forexample, eight levels could be used for ground level followed by sevenlevels increasing 50 feet each followed by eight levels increasing byfeet each, 15 levels increasing by feet each, 20 levels of feet each,and finally 30 levels of 200 feet each.

Thus the system could be used simultaneously for low level flightincluding terrain avoidance, for medium altitude and high altitudeflight. The system thus would be able to adequately simulate thecapability of advanced radar systems.

The number of gray levels described for the reflectivity plate and theelevation plate as well as the number of groups described for thereflectivity plate are examples only. Depending on the specific purposeof the simulation system plates and its desired characteristics,selection of the plate emulsion has to be made which is compatible withthe design parameters of the simulation system.

What is claimed is: 1. In a radar landmass simulator having a firstmemory for storing radar reflectivity information and a second memoryfor storing terrain elevation information to be displayed on a radardisplay, the improvement comprising:

a first memory modified to store both reflectivity information andadditional elevation information,

means for reading out said reflectivity information and said additionalelevation information from said first memory and said elevationinformation from said second memory simultaneously,

combining means for combining said additional elevation information andsaid elevation information into combined elevation information. and

means for transmitting said combined elevation information to said radardisplay to increase the range of elevations displayed.

2. The apparatus of claim 1,

wherein said elevation information is comprised of a selected number ofdiscrete signal levels and wherein said combined elevation informationis comprised of a number of discrete signal levels greater than saidselected number.

3. The apparatus of claim 2,

verter, said reflectivity signals to said radar display and saidcombined elevation information to said radar display, the arrangementbeing such that the number of discretely different reflectivity signalstransmitted to said radar display is less than the storage capacity ofsaid first memory and the number of discrete signal levels in saidcombined elevation information transmitted to said radar display isgreater than the storage capacity of said second memory.

s a: v =0: r

1. In a radar landmass simulator having a first memory for storing radarreflectivity information and a second memory for storing terrainelevation information to be displayed on a radar display, theimprovement comprising: a first memory modified to store bothreflectivity information and additional elevation information, means forreading out said reflectivity information and said additional elevationinformation from said first memory and said elevation information fromsaid second memory simultaneously, combining means for combining saidadditional elevation information and said elevation information intocombined elevation information, and means for transmitting said combinedelevation information to said radar display to increase the range ofelevations displayed.
 2. The apparatus of claim 1, wherein saidelevation information is comprised of a selected number of discretesignal levels and wherein said combined elevation information iscomprised of a number of discrete signal levels greater than saidselected number.
 3. The apparatus of claim 2, said combining meansincluding a reflectivity scale converter for converting saidreflectivity information and said additional elevation information intoa number of reflectivity signals and a number of group signals, and anelevation scale converter for combining said elevation information andsaid group signals into said combined elevation information.
 4. Theapparatus of claim 3 and including connecting means for transmittingsaid group signals from said reflectivity scale converter to saidelevation scale converter, said reflectivity signals to said radardisplay and said combined elevation information to said radar display,the arrangement being such that the number of discretely differentreflectivity signals transmitted to said radar display is less than thestorage capacity of said first memory and the number of discrete signallevels in said combined elevation information transmitted to said radardisplay is greater than the storage capacity of said second memory.